As is known from DE 20 2005 011 686 U1, the ends of the two hot wire coils, which are away from the terminals, may be connected to one another by a coil section, which is led around a lower deflecting edge of the insulating material wall. The insulating material wall is used in this prior-art cartridge type heater only to keep the two coil strands mutually spaced apart from one another and thus to electrically insulate them against each other. To keep the coil strands also away from the metal jacket, special, strap-like spacers are provided, which are arranged at more or less great distances and are fastened to the edges of the insulating material wall in a self-holding manner. The filling of the metal jacket with, for example, granular MgO, into which metal jacket the insulating material wall with the two coil strands had already been inserted, is carried out essentially in the vertical position of the metal jacket with the open upper end. The hot wire ends located in the area of this open end of the metal jacket or the terminal connectors connected to these hot wire ends must now be fixed by means of auxiliary means in order to prevent them from interfering with the filling operation, on the one hand, and to prevent them from entering the metal jacket, on the other hand. It is only after filling in the granular material that the metal jacket can be closed by means of a plug, which also has to receive the terminal connector. This working method is very time-consuming and hence cost-intensive.
A compacted cartridge type heater of this class is also known from DE 70 31 974 U. Two or more hot wire coils (heating conductor coils) with different wire thicknesses and different coil diameters are accommodated in this cartridge type heater concentrically with one another lying exposed in a cylindrical cartridge housing, which has a fixed front-side bottom at one end and whose other end is closed by a metal disk with wart-like holes. Instead of the otherwise usual terminal bolts, strands provided with insulating jackets are connected here within the cartridge housing to the ends of the hot wires. These strands are led with their insulating jackets through the metal disk to the inside, so that there is an insulation between the metal disk and the conductor wires of the strands. Means which insulate the coaxial strands of the coil against each other and against the metallic cartridge housing are not provided. The filling in of the granular insulating material is cumbersome and expensive in this cartridge type heater as well.
An electric jacket tube heating body with integrated temperature sensor, in which the hot wire coils are placed in the metallic jacket tube in a hairpin-like manner and the terminal of the heating conductor is led out at one end of the metallic jacket tube and the terminals of the terminal temperature sensor at the other end of the jacket tube, is known from DE 197 16 010 C1. The two strands of the hot wire coil, which extend in parallel to one another, are embedded in compacted insulating material without a partition. It is necessary here to fill the originally granulated insulating material into the two legs of the metallic jacket tube bent in the shape of a U before the ends of the jacket tube are closed with closing plugs.
No support elements, which would ensure that the windings of the heating coil do not come into contact with the tube wall when the insulating granular material is being filled in, are provided for the hot wire coil within the metal tube in these prior-art cartridge type heaters. It is rather to be ascertained during the filling in of the granular material that the hot wire coils are not bent out and are kept away in space from the tube jacket. This makes it difficult to fill in the granular material and causes high manufacturing costs.